Method of preparation of lubricating oils



June 23', 1970 w, R, K N ETAL 3,516,928

' METHOD OF PREPARATION OF LUBRICATING OILS Filed Feb. 21, 1967-INVENTORS WILLIAM RONALD KING WILLIAM LLEWELYN THOMAS BY MORGAN,FINNEGAN, DURHAM 8| PINE ATTORNEYS United States Patent Office 4/ 6 Int.Cl. Bllld 17/00 US. Cl. 208-308 2 Claims ABSTRACT OF THE DISCLOSURE Amethod is described in which a naphthenic petroleum feedstock boilinga'bove 300 C. and of low n-paraffin content (desirably having a cloudpoint of less than --30 F.) is contacted with a gas at super-criticaltemperature and pressure. Naphthenes are absorbed into the gas phase andmay be extracted therefrom.

This invention relates to a method of preparation of lubricating oilbase stocks, using a super-critical gas phase separation technique.

Dutch published patent application No. 6404125 refers to the use of agas at super-critical temperature and pressure to separate theconstituents of a mixture of liquid and/or solid substances. Theseconstituents may be absorbed to varying extents in the super-criticalgas, and may be separated therefrom by lowering the pressure and/orincreasing the temperature.

This Dutch specification refers in general terms to the separation ofpetroleum or petroleum products into their constituents. Elsewhere it isstated that the absorbability of the constituents of the treatedmaterial can be related to the volatility of these constituents, themore volatile substances being absorbed into the super-critical gas morereadily than the less volatile substances.

We have found that absorbability in certain cases is not dependent onthe volatility of the compound taken up into the gas phase as such, butrather to the molecular structure of the compound. Thus it has beenfound that contacting a naphthenic crude petroleum or a petroleumfraction derived from a naphthenic crude with a supercriticalhydrocarbon gas resulted in preferential absorption by the gas of thenaphthenic materials. Lubricating oils may desirably have a high contentof naphthenes and the present process therefore provides a means bywhich base stocks suitable for the preparation of lubricating oils andgreases may be prepared. Since. n-parafiins may be absorbedpreferentially to naphthenes by a gas under super-critical conditions oftemperature and pressure, the feedstock should have a low n-paraftin orwax content. Preferably it should have a cloud point of less than 30 F.If necessary reduction in wax or n-paraffin content to this level maybe. achieved by conventional solvent or catalytic dewaxing procedures,or by the technique using a gas under super-critical conditions oftemperature and pressure disclosed in our co-pending British patentapplication No. 7,682/66.

The method of the invention produces a material of reduced sulphurcontent compared to the original feedstock. If a product of low sulphurcontent is required, then a low sulphur feedstock should be. used.Conversely, a material of moderate sulphur content may be desirable as abase stock for certain lubricant applications, and in this case afeedstock having a suitably higher sulphur content should [be chosen.The materials obtained will boil within the range 350-590 C., dependingon the boiling range of the feedstock.

3,516,928 Patented June 23, 1970 The invention accordingly consists in amethod of preparing a petroleum material of greater naphthene contentthan the original feedstock which comprises contacting a naphthenicfeedstock boiling above 300 C. and, of low nparaflin content with a gasunder super-critical conditions of temperature and pressure, removingthe gas phase product, and separating therefrom a material enriched innaphthenes.

Subject to the above requirements the feedstock may be a crude petroleumor a fraction derived therefrom. The fraction treated may be derivedfrom the crude petroleum by conventional distillation, or super-criticalmeans may be employed. In the latter case the crude petroleum may beseparated into light and heavy fractions and the latter contacted withsuper-critical gas at lower pressure and higher temperature than in theinitial separation.

The choice of gas used in a super-critical separation process, and the.temperature and pressure at which it is used, will depend on thecomponents to be separated. Thus, the gas must be inert with respect tothe components to be separated. Since absorbability is greater thenearer the process temperature is to the critical temperature of the gasand the greater is the process pressure, it is desirable. that a gas bechosen whose critical temperature is near, but below, the desiredworking temperature, and whose critical pressure is, as far as possible,much below the desired working pressure. The working temperature shouldnot be more than C. above the critical temperature. In addition it ispreferable that the working temperature should be within the range -100C. to +300 C., and that the boiling point of the feedstock should be atleast 100 C. above the critical temperature of the gas. Taking these,and other criteria, into account, suitable gases for use in the methodof the present invention include the lower alkanes and alkenes and theirhalogenated derivatives, and inorganic gases such as carbon dioxide andammonia. Mixtures of one or more of these gases may be used providedthat they are inert with respect to the feedstock. For the separation ofhydrocarbon mixtures such as are envisaged in the present applicationthe gases ethane, ethylene, propane, and propylene are especiallypreferred.

The experimental work on which this invention was based was carried outin the apparatus shown diagrammatically in the drawing. This comprises avisual cell 1 of 180 ml. capacity which is a flanged stainless steelcylinder capable of withstanding pressures of up to 10,000 p.s.i., andfitted with a sight glass along its entire length, connected at its topvia nylon tubing and a valve 3 to a small glass graduated receiver 4,fitted with a side arm and a valve 5. The side arm is connected to a gasmeter 13, the gas from which is vented to atmosphere, or compressed andrecirculated to the system. The bottom of the cell is connected by highpressure small bore tubing via a valve 2 and another valve 8 to the topof a gas cell 7 containing mercury. The gas cell is connected via avalve 9 to a mercury pump '10 fitted with a pressure gauge 11. Gas issupplied from cylinder 12. The pump is an electrically driven positivedisplacement device of conventional design. The visual cell and thereceiver, together with the associated valves 2, 3' and 5, are locatedin an electrically heated and thermostatically controlled air oven 6fitted with a window and means for applying slight agitation to thecell.

In carrying out the work, 50 ml. of the feedstock was charged to thevisual cell through the open top. The top flange was then replaced andthe cell evacuated with a vacuum pump so as to deaerate the system asmuch as possible. The temperature of the air oven was then set at thedesired value, and gas, compressed as desired by the mercury pump to thedegree indicated by the pressure gauge was introduced into the visualcell from the gas cell by opening valve 2 slightly, valves 8 and 9 beingopen and valves 3 and 5 being closed. The introduction of gas was keptat a low rate, valve 2 being opened gradu ally until fully opened, thepressure in the gas cell being kept constant during this period byoperation of the mercury pump. When valve 2 Was fully open valves 8 and9 were closed and the visual cell was agitated to promote equilibriumbetween the gas and liquid phases. More gas was introduced as foundnecessary to maintain a constant pressure. The procedure was repeateduntil the pressure has been stabilized.

Gas was now allowed to bubble through the liquid in the visual cell byopening valve 3 so as to permit a flow rate of 2 to 3 litres per minuteas measured by the gas For comparison a conventonal vacuum distillationwas carried out on the same feedstock as was treated in the abovemanner, a Vacuum Engler apparatus being used.

EXAMPLE TABLE 1 [Super-critical gas phase separation of Bachaquero 76.9%wt. residue with ethane at 176 F. and 5,000 p.s.i.g.]

Inspection data Product Cnmula- Product yield, tive Mid, rate. g./l00Specific Sulphur Kinematic viscosity, Wax Asphalpercent percent normgravity, content, cst. at- Four content, tones, wt. on wt. yield litres60 F./ percent point, percent percent Fraction No. feed on feed ethane60 F. wt. 100 F. 140 F. 170 F. 210 F. VI wt. wt.

1 Calculated.

TABLE 2.VAC UUM ENGLE R DISTILLATION OF BACIIAQUE R0 76.9% WT. RESIDUEInspection data TBP Sulphur Kinematic viscosity, cst. at- Wax Asphal-Tempercontent. Pour content, tencs, Fraction ature, percent 100 140 170210 point, percent perce it 0. wt. F. F. F. F. VI F. wt. wt.

Feed i 516 1111?E2366 iiV LiiIIIIIIIIIIIIIIIIII "if-i "ifs 1 Calculated.

meter. The pressure of the gas in the tubing connecting valve 3 to theproduct receiver under these circumstances fell to atmospheric, and anymaterial which has been taken up into the gas phase was therebyprecipitated and carried by the gas to the receiver. The requiredquantity of material was allowed to accumulate in the receiver and theflow of gas then stopped. A short time was allowed to elapse for liquidin the tubing to drain into the receiver. The fraction thus collectedwas removed for examination and further fractions obtained by resumingthe gas flow and repeating the procedure described.

When necessary the product rate was increased by raising the pressuse inthe visual cell progressively. In this case the gas flow was interruptedand the system allowed to reach equilibrium at the higher pressure.

At the end of each experiment valve 2 was closed and valve 3 graduallyopened so as to bring the pressure in the visual cell down toatmospheric. In the cases where the residue remaining in the cell wasfluid it was drained through valve 2 after disconnecting from valve 8.Otherwise the top flange of the visual cell was removed and the materialdissolved in a low boiling hydrocarbon solvent and removed. With thismaterial was combined material, if any, which had collected in thereceiver during de-pressurisation of the visual cell. The solvent wasstripped otf conventionally in a stream of nitrogen.

A material balance for each experiment was made by weighing the quantityof feedstock charged to the cell, and also each of the gas phasefractions and the residue.

The product rate was expressed as the weight of material vaporised perunit volume of gas measured at NTP.

It will be seen that the fractions obtained with supercritical ethaneare considerably more naphthenic in character than the correspondingdistillates. This is revealed by the substantially higher viscosityindices of the former than of the latter, as to which, on a calculatedbasis, the calculated viscosity indices for the bulked super criticalgas phase fractions and the Vacuum Engler distillates are +16 and 17,respectively.

The super-critical gas phase products have slightly lower sulphurcontents than the corresponding distillates and they also have lowasphaltene contents. In addition, and although not shown in Table 1,their colour was better than that of the distillate fractions. All thesecharacteristics are desirable in a lubricating oil base stock, and sucha stock can be obtained as has been described without the need to uselarge quantities of liquid solvents or catalytic methods usingrelatively arduous conditions.

We claim:

1. A method of obtaining naphthenic lubricating oil base stock having agreater naphthene content than the original feedstock from a naphthenicfeedstock having a low n-paraflln content in one stage without any needfor further processing which comprises contacting the naphthenicfeedstock boiling above 300 C. and having a low n-paraffin content and acloud point of less than 30 F., with a gas selected from the groupconsisting of lower alkanes, lower alkenes, and halogenated derivativesthereof at a working temperature and a working pressure'above thecritical temperature and the critical pressure of said gas, said workingtemperature being within the range C. to 300 C. and not more than 100 C.above the critical temperature of said gas and said working pressurebeing greater than the critical pressure of said gas, said gas beinginert with respect to the components to be separated, removing a gasphase product, and separating therefrom a lubricating oil base stockenriched in naphthenes.

2. A method of obtaining naphthenic lubricating oil base stock having agreaternaphthene content than the original feedstock from a naphthenicfeedstock having a low n-parafiin content in one stage without any needfor further processing which comprises contacting the naphthenicfeedstock boiling above 300 C. and having a low n-paraffin content and acolud point of less than --30 F., with a gas selected from the groupconsisting of ethane, ethylene, propane, propylene, carbon dioxide,ammonia, and their inert mixtures thereof at a working temperature and aworking pressure above the critical temperature and the criticalpressure of said gas, said working temperature being within the range100 C. to 300 C. and not more than 100 C. above the critical temperatureof said gas and said working pressure being greater than the criticalpressure of said gas, said gas being inert with respect to thecomponents to be separated, removing a gas phase product, and separatingtherefrom a lubricating oil base stock enriched in naphthenes.

References Cited UNITED STATES PATENTS 2,391,576 12/1945 Katz et a1208-366 2,391,607 12/1945 Whaley 208356 HERBERT LEVINE, Primary ExaminerUS. Cl. X.R. 208309, 366

June 23, 1970 Patent No. 3,516,928 Dated Inventor-(a) William RonaldKing and William Llewelyn Thomas It is certified that error appears inthe above-identified patent and that said Letters Patent are herebycorrected as shown below:

Column 1, line 18 for "-30F" read --30F--;

Column 3, Table 2, column headed "Specific Gravity 60F./60F." line 3 for"9.957" read --0.057-; line 4 for "9.972" read --o.972--;

SIGNED AND CALEB Ilium (SEAL) Edward M. Fletcher, Ir. Attcsting Officermums 1:. m. Oomissiom of Patents

